Ophthalmic surgery frequently involves the removal of fluid and/or tissue from the eye and replacement of the material removed with a fluid such as a balanced salt solution (BSS). In order to remove material, a cannula connected to an aspiration line is inserted into an incision in the eye. The aspiration line is coupled to a console that includes electronics, a control system, a vacuum source such as a peristaltic pump and a fluid source. The vacuum source provides a vacuum to the aspiration line. The vacuum in the aspiration line causes material to flow from the eye and through the aspiration line. To maintain intraocular pressure, another cannula connected to an irrigation or infusion line is inserted into another incision in the eye. The irrigation line is connected to a fluid source in the console. The fluid source may be a reservoir of BSS that can be pressurized to greater than the ambient pressure. When the fluid source is pressurized, the fluid flows is forced out of the fluid source, through the irrigation line and into the eye.
During such surgery, it is desirable to isolate biological material removed from the eye from the vacuum pump. To do so, cassettes are used. A cassette typically fits within a receptacle within the console. Tubing from the aspiration line is connected to a port in the cassette. The cassette is connected to the vacuum source via another port. The vacuum source applies a vacuum to the cassette, which provides the vacuum to the aspiration line. The suction in the aspiration line causes biological material to flow from the eye into the cassette, where the biological material is stored. Thus, the biological material is isolated from the vacuum pump. To provide fluid to the eye, another cassette coupled to a pressure or fluid source and to the irrigation line may be used in an analogous manner.
A pressure sensor may be used to monitor pressure within the cassette during use. For example, a rubber membrane may flex in response to the internal pressure of the cassette. This deflection may cause the membrane to touch a contact sensor. Thus, the pressure may be determined. Alternatively, a sensor may provide light that is reflected off of the membrane at an oblique angle. The reflected light is provided to a sensor. Changes in the position of the light correspond to changes in the internal pressure.
There may be drawbacks to such mechanisms for measuring internal pressure of the cassette function. For example, use of reflected light may not provide sufficiently sensitivity to the internal pressure. Further, the flexible membrane adds to the cost of each of the cassettes, which are disposable. Internal pressure sensors may be subject to the biological material removed from the eye. Thus, such sensors may fail. These sensors also add to the cost of the disposable cassettes.
Accordingly, what is needed is an improved mechanism for monitoring the internal pressure of a cassette in a surgical system.